1. Technical Field
This invention relates generally to constant velocity joints and more particularly to stroking tripot joints wherein a set of flat balls mounted on respective trunnions of a shaft assembly stroke and pivot within associated longitudinal ball channels of a tripot housing.
2. Related Art
Half shaft assemblies are typically used in automotive drive line applications, and particularly in front wheel drive applications to transmit torque from the transmission or transfer case to the drive wheels of the vehicle. The half shaft assembly typically comprises a rigid shaft fitted with constant velocity joints at its ends. A stroking tripot joint is typically used at the inboard end where the shaft assembly couples to the transmission or transfer case. The tripot joint is effective at permitting both pivoting angular movement and a certain amount of axial movement to accommodate adjustment in the effective length of the shaft assembly during operation.
A typical tripot joint includes a tripot housing having three longitudinally extending ball channels. The housing has a stub shaft or splined sleeve extending from a closed end which connects with the transmission of the vehicle. The opposite end of the housing is open to receive a spider carried on the half shaft. The spider includes three radially outwardly extending trunnions which align with the ball channels of the housing. Each trunnion mounts a flat roller ball which is journalled on the trunnion by a plurality of needle bearings. A washer-like ball retainer fits over the free end of the trunnions and is retained by a ring accommodated within a ring groove machined in the running surface of the trunnions adjacent the free end. The ball retainer is able to rotate on the trunnion and projects radially outwardly to confront the bearings and roller ball to prevent the roller balls and needle bearings from being slid off the free end of the trunnions.
The ball retainers and retaining rings thus operate to support the needle bearings and roller balls on the trunnions until such time as the spider assembly is installed within the housing of the joint.
One disadvantage of the present ball retention system is that it adds cost and complexity to the manufacture of tripot joints by requiring the trunnions to be machined to include the retaining grooves and requires the additional components of the ball retainer and retaining ring for each trunnion.
There is also cost in handing and assembling the numerous loose needle bearings about the trunnion shafts and supporting them while installing the roller balls, ball retainers and retaining rings to ensure that they remain in position until the assembly is complete.
An object of the present invention is to overcome or greatly minimize the foregoing limitations of the present ball retention system for tripot joints.
A constant velocity tripot joint according to the invention comprises a tripot housing having a plurality of longitudinally extending ball channels formed therein, a spider having a plurality of trunnions projecting radially outwardly to free ends arranged to be received within the ball channels of the housing. The assembly includes a plurality of ball modules formed as a separate, self-supporting structure from the trunnions and disposed thereon for receipt in the ball channels. Each ball module includes a flat roller ball having a bore, a plurality of needle bearings disposed within the bore, and a bearing cage coupled to the roller ball and supporting the needle bearings within the bore in rolling engagement with an inner surface of the bore.
Unlike the standard tripot joints described above, tripot joints constructed according to the invention include the described ball modules which are formed as a separate preassembled unit apart from the trunnions. In this manner the assembly and construction of the joint is simplified by enabling the ball modules to be installed on the trunnions at a point just prior to the assembly of the spider into the housing. By providing a ball cage which retains the roller bearings within the bore of the roller balls, there is no longer the need to machine a retaining groove in each of the trunnions or to provide the ball retainer and retaining ring components for each trunnion as previously described.
The invention recognizes the advantages of preassembling the bearings with the roller balls rather than on the trunnions which enables the ball modules to be separately manufactured and supplied as a pre-manufactured, self-contained component and which is no longer dependent for support on the ball retainer and retaining rings.
The invention further recognizes that the roller balls and bearings, once installed within the ball channels, are supported against removal from the trunnions by the walls of a housing, and thus there is no need for longitudinal retention between the tunnion and the needle bearings and/or roller balls. A further advantage of the invention is that the roller balls are free floating in the longitudinal direction of the trunnions and thus the movement of the joint is not restricted by interference between longitudinal displacement of the roller balls and confrontation with any ball retainers or retaining rings of prior joint assemblies.
The roller cage preferably includes two or more webs or struts extending along the inner surface of the roller ball which separate the roller bearings into groups and help guide and support the roller bearings during rotation of the roller balls to keep the roller bearings aligned in the longitudinal direction of the trunnions.
The invention further provides a method of making a tripot joint including providing a spider having a plurality of radially outwardly extending trunnions that fit within longitudinally extending ball channels of a tripot housing, and forming a plurality of ball modules each including a roller ball having a plurality of needle bearings disposed within a bore of the roller ball and a bearing cage mounted to the roller ball to retain the needle bearings within the bore. The method includes disposing one of the ball modules on each of the trunnions and then extending the trunnions and roller ball modules into respective ball channels of the housing. The method shares the same advantages described above over prior tripot joints and manufacturing methods.